Legal Glossary

Plain-language definitions of 50 legal terms, each linked to the statutes and cases where the term does its work.

• Adverse Possession A doctrine by which someone who openly occupies another's land without permission for a statutory period, often 10 to 20 years, can acquire legal title to it. The possession must be actual, exclusive, open and notorious, hostile to the owner's rights, and continuous for the full period. The rule pushes owners to police their boundaries and quiets stale disputes over long-settled land use.
• Attorney-Client Privilege A rule protecting confidential communications between a client and lawyer made for the purpose of seeking or giving legal advice. The privilege belongs to the client, survives the client's death, and cannot be overridden merely because the information is important to the other side. It can be waived by sharing the communication with outsiders, and it does not protect communications made to further a crime or fraud.
• Breach of Contract The failure to perform a contractual obligation without a legal excuse. A material breach goes to the heart of the bargain and can excuse the other side from performing, while a minor breach entitles the injured party to damages but keeps the contract alive. The usual remedy is money damages designed to put the injured party where performance would have left it.
• Burden of Proof The obligation to prove the facts supporting a claim or defense to the required degree of certainty. In most civil cases the standard is a preponderance of the evidence, meaning more likely than not; some issues like fraud require clear and convincing evidence; criminal convictions require proof beyond a reasonable doubt. The burden generally rests on the party asserting the claim.
• Business Judgment Rule A presumption that corporate directors acted on an informed basis, in good faith, and in the honest belief their decision served the company's best interests. Courts applying the rule will not second-guess a board's business decisions, even bad ones, unless the challenger shows fraud, conflict of interest, or gross inattention. It protects reasonable risk-taking and keeps judges out of the boardroom.
• Class Action A lawsuit in which one or a few named plaintiffs sue on behalf of a larger group of similarly situated people. A court must certify the class, finding among other things that common questions predominate and the representatives will adequately protect absent members. Class actions make it economical to pursue claims that would be too small to litigate individually.
• Collateral Estoppel A doctrine, also called issue preclusion, that prevents a party from relitigating a specific factual or legal issue that was actually decided against it in a prior case, even if the new lawsuit involves a different claim. The issue must have been actually litigated, necessarily decided, and essential to the earlier judgment. Unlike res judicata, it targets individual issues rather than whole claims.
• Consideration The bargained-for exchange of value that makes a promise legally enforceable as a contract. Each side must give or promise something, whether money, goods, services, or giving up a legal right; a gratuitous promise generally is not a contract. Courts rarely question whether the exchange was a good deal, only whether a real exchange occurred.
• Copyright The exclusive legal rights of authors in original works fixed in a tangible medium, including books, software, music, photographs, and films. Protection arises automatically upon creation, though registration is required before a U.S. author can sue and unlocks statutory damages. Copyright protects expression, not the underlying ideas, facts, or methods.
• Defamation A false statement of fact about a person, communicated to a third party, that harms the person's reputation. Written defamation is libel and spoken defamation is slander; opinions and true statements are not actionable. Public figures must additionally prove actual malice, meaning the speaker knew the statement was false or recklessly disregarded the truth.
• De Novo Latin for anew, describing review in which a court decides an issue fresh, giving no deference to the decision below. Appellate courts review pure questions of law de novo, while factual findings usually receive a more deferential standard. The term also describes trials conducted from scratch after certain lower-tribunal proceedings.
• Deposition Sworn out-of-court testimony taken before trial, usually in a conference room with a court reporter and sometimes a videographer. Lawyers question the witness under oath, and the transcript can be used to prepare for trial, support motions, or impeach the witness if their story changes. Depositions are often the single most important discovery tool in commercial litigation.
• Discovery The pretrial phase in which parties formally exchange evidence and information relevant to the claims and defenses. Tools include document requests, interrogatories, depositions, and requests for admission, all subject to proportionality limits and privilege protections. Discovery is where most civil cases are won, lost, or settled.
• Due Process The constitutional guarantee that the government cannot deprive a person of life, liberty, or property without fair procedures, and, under the substantive branch, without adequate justification. Procedural due process typically requires notice and a meaningful opportunity to be heard before deprivation. The guarantee binds the federal government through the Fifth Amendment and the states through the Fourteenth.
• Easement A legal right to use another person's land for a specific purpose without owning it, such as a driveway crossing a neighbor's parcel or a utility line running beneath it. Easements can be created by written grant, by necessity, or by long-continued use, and many run with the land, binding future owners. The landowner keeps full ownership but cannot interfere with the easement holder's permitted use.
• Fair Use A defense to copyright infringement that permits limited use of protected works for purposes like criticism, commentary, news reporting, teaching, and research. Courts weigh four factors: the purpose and character of the use, the nature of the work, the amount taken, and the effect on the market for the original. Transformative uses that add new meaning or purpose are the most likely to qualify.
• Fiduciary Duty The highest duty the law imposes, requiring a person entrusted with another's interests, such as a corporate director, trustee, agent, or partner, to act with loyalty and care for the beneficiary rather than for personal gain. The duty of loyalty forbids self-dealing and conflicts of interest; the duty of care requires informed, diligent decision-making. Breaches can support damages, disgorgement of profits, and removal.
• Habeas Corpus A judicial procedure, literally meaning that you have the body, by which a person in custody challenges the legality of their detention. The writ compels the custodian to bring the prisoner before a court and justify the confinement. Rooted in English law and preserved in the U.S. Constitution, it is a core safeguard against unlawful imprisonment.
• Hearsay An out-of-court statement offered in evidence to prove the truth of what it asserts, which is generally inadmissible because the person who made it cannot be cross-examined. The rule is riddled with exceptions, including business records, excited utterances, and statements by an opposing party. A statement offered for another purpose, such as showing notice or state of mind, is not hearsay at all.
• Injunction A court order requiring a party to do something or, more commonly, to stop doing something. Preliminary injunctions preserve the status quo during litigation, while permanent injunctions issue after a final ruling; both generally require showing irreparable harm that money damages cannot fix. Violating an injunction can result in contempt sanctions.
• Interrogatories Written questions one party sends another during discovery, which must be answered in writing and under oath within a set time. They are useful for locking in basic facts, identifying witnesses and documents, and pinning down the other side's contentions. Most courts cap the number a party may serve without permission.
• Liquidated Damages A contract provision fixing in advance the amount payable if a party breaches, used when actual damages would be hard to prove. Courts enforce these clauses if the amount was a reasonable forecast of likely harm, but strike them down as unenforceable penalties if they are designed to punish rather than compensate. They are common in construction, real estate, and confidentiality agreements.
• Mens Rea The mental state a defendant must have for criminal liability, literally the guilty mind. Statutes grade culpability from intentional and knowing conduct down to recklessness and criminal negligence, and the required level often separates serious offenses from lesser ones. A few regulatory offenses dispense with mens rea entirely and impose strict liability.
• Motion to Dismiss An early request asking the court to throw out a lawsuit, or particular claims, before the parties exchange evidence. The most common version argues that even if everything in the complaint is true, it does not state a legally recognized claim. Other versions attack the court's jurisdiction, the venue, or defects in how the suit was served.
• Negligence The failure to use the care a reasonably prudent person would use in similar circumstances, resulting in harm to another. A plaintiff must prove four elements: a duty of care, breach of that duty, causation, and damages. It is the backbone of most personal-injury and professional-malpractice litigation.
• Parol Evidence Rule A rule that, when parties adopt a written contract as the final expression of their deal, bars evidence of earlier or contemporaneous oral agreements that would contradict or add to the writing. It protects the integrity of integrated written agreements, which is why contracts include merger or entire-agreement clauses. Evidence remains admissible for limited purposes such as proving fraud or clarifying genuine ambiguity.
• Patent A government grant giving an inventor the right to exclude others from making, using, or selling an invention for a limited term, generally 20 years from filing for utility patents. In exchange, the inventor must publicly disclose how the invention works in enough detail for others to practice it. To be patentable, an invention must be novel, non-obvious, and directed to eligible subject matter.
• Personal Jurisdiction A court's power over a particular defendant, which generally requires that the defendant have sufficient contacts with the state where the court sits. A company can be sued where it is at home, or where it purposefully directed activities that gave rise to the claim. Without personal jurisdiction, any judgment against the defendant is void.
• Piercing the Corporate Veil An equitable doctrine allowing courts to disregard a corporation's separate legal existence and hold its owners personally liable for company debts. Courts pierce the veil when owners ignore corporate formalities, commingle funds, undercapitalize the business, or use the entity to perpetrate fraud or injustice. It is an exception to limited liability, applied sparingly and usually against closely held companies.
• Prima Facie Latin for at first sight, describing evidence that, if unrebutted, is sufficient to establish a fact or claim. A prima facie case is the minimum showing on each element that gets a claim to the fact-finder and shifts the practical burden to the other side to respond. It does not mean the claim will win, only that it clears the initial threshold.
• Prior Art The body of publicly available knowledge, including earlier patents, publications, products, and public uses, that existed before a patent application's effective filing date. An invention cannot be patented if the prior art already discloses it or makes it obvious to a person skilled in the field. Accused infringers routinely hunt for prior art to invalidate the patents asserted against them.
• Promissory Estoppel A doctrine that enforces a promise even without a formal contract when the promisor should have expected the promise to induce reliance, the other party reasonably relied on it, and injustice can only be avoided by enforcement. It functions as a safety valve where consideration or other contract formalities are missing. Recovery is often limited to the losses caused by the reliance.
• Proximate Cause The legal limit on how far liability extends from a wrongful act, asking whether the harm was a foreseeable result of the defendant's conduct. Even if a defendant factually caused an injury in a but-for sense, there is no liability if the chain of events was too remote or bizarre to anticipate. It keeps defendants from being liable for every distant ripple of their conduct.
• Res Judicata A doctrine, also called claim preclusion, that bars parties from relitigating a claim that was already decided by a final judgment on the merits. It applies not only to claims actually raised but also to claims that could have been raised in the earlier case arising from the same transaction. The rule protects finality and prevents parties from getting two bites at the apple.
• Respondeat Superior A doctrine making employers vicariously liable for torts their employees commit within the scope of employment. The injured party need not show the employer did anything wrong itself; liability attaches because the employee was doing the employer's work when the harm occurred. It generally does not cover independent contractors or employees on a purely personal frolic.
• Specific Performance An equitable remedy ordering a breaching party to actually perform the contract rather than just pay damages. Courts grant it only when money is inadequate, most classically for sales of land or unique goods like artwork or a controlling block of stock. It is generally unavailable for personal-services contracts, which courts will not force people to perform.
• Stare Decisis The principle that courts should follow their own prior decisions and those of higher courts when deciding similar cases, meaning to stand by things decided. It gives the law stability and predictability while still allowing courts to overrule precedent for compelling reasons. Lower courts are strictly bound by higher-court precedent; a court's adherence to its own precedent is a strong but rebuttable practice.
• Statute of Frauds A rule requiring certain categories of contracts to be evidenced by a signed writing to be enforceable, including contracts for the sale of land, agreements that cannot be performed within one year, and sales of goods above a threshold amount. The writing need not be formal, but it must capture the essential terms and be signed by the party being sued. Partial performance and other exceptions can take an oral deal outside the statute.
• Statute of Limitations A law setting the deadline for filing a lawsuit, measured from when the claim accrued, which is usually when the injury occurred or was discovered. Miss the deadline and the claim is barred no matter how strong it is, though doctrines like tolling and the discovery rule can extend the clock. Different claims carry different periods, often ranging from one to six years.
• Strict Liability Liability imposed without proof of fault or intent, based on the nature of the activity or product rather than the defendant's care. It applies to abnormally dangerous activities like blasting, to keeping wild animals, and most importantly to defective products that injure users. The plaintiff still must prove the defect or activity caused the harm.
• Subpoena Duces Tecum A court-backed command requiring a person or organization, often a non-party, to produce documents, records, or other tangible things. It differs from an ordinary subpoena, which compels only testimony. Recipients can object or move to quash if the demand is overbroad, seeks privileged material, or imposes an undue burden.
• Summary Judgment A procedural device that lets a court decide a case, or part of one, without a trial when the key facts are not genuinely in dispute. The moving party must show that no reasonable jury could find for the other side on the evidence in the record, entitling the movant to judgment as a matter of law. Courts view the evidence in the light most favorable to the non-moving party.
• Tortious Interference A tort committed when someone intentionally and improperly disrupts another's contract or business relationship, causing economic harm. Interference with an existing contract is the classic form; interference with a prospective business relationship is also actionable but requires more egregious conduct. Ordinary competition is a defense, so the interference must involve wrongful means or purpose.
• Trademark A word, name, logo, or other symbol that identifies the source of goods or services and distinguishes them from competitors. Rights arise from actual use in commerce, and federal registration adds significant procedural and remedial advantages. Infringement turns on whether consumers are likely to be confused about source, sponsorship, or affiliation.
• Trade Secret Information that derives economic value from not being generally known and that its owner takes reasonable measures to keep secret, such as formulas, algorithms, customer lists, or manufacturing processes. Protection lasts as long as secrecy is maintained, but is lost if the information leaks or is independently discovered. Misappropriation, acquiring or using a secret through improper means, is actionable under both state law and the federal Defend Trade Secrets Act.
• Unconscionability A defense that lets courts refuse to enforce a contract or clause that is grossly unfair. It usually requires both procedural unfairness, such as fine print, no meaningful choice, or unequal bargaining power, and substantive unfairness in the terms themselves. Courts may void the whole agreement or simply strike the offending term.
• Venue The particular court location, among those with jurisdiction, where a case may properly be heard. Venue rules typically point to where the defendant resides or where the events at issue occurred, and a court may transfer a case to a more convenient forum. Venue is about the right courthouse; jurisdiction is about the court's power.
• Voir Dire The process of questioning prospective jurors to uncover bias and decide who will sit on the jury. Lawyers and the judge probe jurors' backgrounds and opinions, and each side may strike jurors for cause or use a limited number of peremptory strikes. The term also describes preliminary questioning of a witness, often an expert, to test qualifications before testimony.
• Work Made for Hire A copyright doctrine under which the employer or commissioning party, not the human creator, is treated as the author and owner from the moment of creation. It covers works created by employees within the scope of their jobs, and certain specially commissioned works if the parties agree in a signed writing. Independent-contractor work usually does not qualify automatically, which is why contracts pair work-for-hire language with a backup assignment.
• Work Product Doctrine A protection shielding materials prepared by or for a party in anticipation of litigation from discovery by the opposing side. Ordinary work product, like witness interview memos, can be obtained only on a showing of substantial need, while a lawyer's mental impressions and legal strategies receive nearly absolute protection. It is broader than attorney-client privilege in covering non-communications, but narrower in requiring a litigation purpose.